Aljazeera quoted Mehlis, addressing a press conference in New York on Friday, as saying that the names of the Syrians had been removed on presumption of their innocence.
He made the deletions under no pressure from any party, Mehlis added.
The 53-page report the veteran German prosecutor sent to the Security Council late on Thursday accused Syrian officials and their Lebanese allies of hatching an intricate scheme to kill al-Hariri and 20 others in a 14 February truck bombing in Beirut.
Perhaps the most explosive section of the report described an account of the plotting given by an unidentified Syrian witness.
The witness said that Maher al-Assad, the brother of Syrian President Bashar al-Assad, and the president's brother-in-law, Major-General Asef Shawkat, were among a group of Syrian and Lebanese security officials who "decided to assassinate" al-Hariri in a mid-September 2004 meeting in Damascus.
But while the names appeared in an early draft of the report, they were removed before the final version was released.
One version of the report circulated at the UN showed the precise details of the computerised editing process, identifying what was deleted and when the edits took place.
The tracking details indicated that the names of Maher al-Assad, Shawkat and others had been deleted at the time Mehlis was meeting on Thursday UN Secretary-General Kofi Annan, who had earlier promised not to edit the report.
Mehlis (L) said he was under no
pressure to edit the report
While Shawkat, widely seen as the No 2 man in the Syrian government, was named in several parts of the report, Maher al-Assad's name appeared only once in the first draft and not at all in the final version.
Mehlis and UN chief spokesman Stephane Dujarric quickly insisted on Friday that the editing had been done by Mehlis himself and not by Annan, who had transmitted the report to the Security Council about seven hours after receiving it from Mehlis.
"This is Mr Mehlis' investigation. This is his report. The secretary-general has at no time made any attempt to influence the report," Dujarric said.
"I would urge you to look towards unfortunate clerical error rather than to conspiracy," Dujarric said.
Mehlis, who plans to brief the Security Council on the report next Tuesday, said any editing changes "resulted from the editorial process carried out by my team, under my direction, and are my responsibility".
"No one outside of the report team influenced those changes. No changes whatsoever were suggested by the secretary-general or by anyone at the United Nations," he said.
Top Lebanese and Syrian officials
are blamed for al-Hariri's killing
US Ambassador John Bolton said the flap was distracting the UN from the report's main findings, which he said showed "clear evidence" of Syrian obstruction of justice
and "probable cause to believe that the assassination could not have been undertaken without the knowledge of senior figures in Syrian intelligence".
"In the absence of serious Syrian cooperation on substantive matters, the mission can't get to the ultimate truth," Bolton said.
The report's substance "doesn't change no matter what version you have", he said.